452 Marsh — New Reptiles from the Laramie Formation. 



hitherto among Dinosaurs, only in the genus Cerato&aurus 

 described by the writer from the Jurassic of Wyoming.* The 

 present pelvis resembles that of Ceratosaurus in its general 

 features, but there is no foramen in the pubis. 



There are five vertebrae in the sacrum, firmly coossified with 

 each other, as are also the sacral spines. The sacral vertebrae 

 are grooved below, with the sides of the centra excavated. 

 The caudals have the diplosphenal articulation, and the first 

 caudal bears a chevron. All the bones preserved are very 

 delicate, and some of them, at least, are apparently pneumatic. 

 The sacrum measures fifteen inches in length, and the twelve 

 caudals following occupy a space of thirty-one inches. The 

 known remains indicate a reptile about eight or ten feet in 

 length. 



In the same horizon occur the remains of a very minute 

 species, which agrees in all its characters, so far as determined, 

 with the members of this genus. The most characteristic 

 portions secured are the metatarsal bones, and these show the 

 same features exhibited in the type species of the genus, O. 

 velox. They are, however, so much smaller as to suggest that 

 they may pertain to a bird. Various portions of the second, 

 third, and fourth metatarsals are known, and the distinctive 

 feature is seen in the third, which has the upper part of the 

 shaft so attenuated that it may not reach to the tarsus. The 

 second and fourth metatarsals are very long and slender. This 

 unique fossil, when alive, was about the size of the common 

 fowl. The species may be called Omithomimus minutus. 



The large species described by the writer as Omithomimus 

 grandis belongs in essentially the same horizon. Portions of 

 two other skeletons have since been obtained, which apparently 

 pertain to this species. In one of these, the femur, tibia, and 

 fibula are in good preservation, and they clearly demonstrate 

 that this reptile was one of the largest of the Theropoda. The 

 femur and tibia have each a very large cavity in the shaft, 

 with well-defined walls. Even the fibula has a cavity in its 

 upper portion. In the other specimen, the second metatarsal 

 is in fair preservation, and shows the same form as in the type 

 of the genus. 



There is much probability that this gigantic carnivore was 

 one of the enemies of the Ceratopsidce, and the discovery of 

 the entire skull and skeleton will be awaited with interest, as 

 they will doubtless show special features for offense, which the 

 peculiar defensive armor of the Ceratopsidw was designed to 

 meet. 



The known remains of all the above species are from the 

 Ceratops beds of Wyoming. 



*This Journal, vol. xxvii, p. 329, April, 1884. 



